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on Insulin-Stimulated Glucose Transport in L6 Myotubes1
J. A. Haley Veterans Hospital Research Service and Department of Internal Medicine, University of South Florida College of Medicine, Tampa, Florida 33612
Address all correspondence and requests for reprints to: Robert V. Farese, M.D., Research Service (VAR 151), J. A. Haley Veterans Hospital, 13000 Bruce B. Downs Boulevard, Tampa, Florida 33612. E-mail: rfarese{at}com1.med.usf.edu
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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potentiated
maximal and half-maximal effects of insulin on 2-deoxyglucose uptake,
but did not alter basal uptake. Expression of constitutively active
PKC- enhanced basal 2-deoxyglucose uptake to virtually the same
extent as that observed during insulin treatment. In contrast,
expression of kinase-defective PKC- completely blocked
insulin-stimulated, but not basal, 2-deoxyglucose uptake. Similar to
alterations in glucose transport, constitutively active PKC-
mimicked, and kinase-defective PKC- completely inhibited, insulin
effects on GLUT4 glucose transporter translocation to the plasma
membrane. Expression of kinase-defective PKC-, in addition to
inhibition of atypical PKC enzyme activity, was attended by paradoxical
increases in GLUT4 and GLUT1 glucose transporter levels and
insulin-stimulated protein kinase B enzyme activity. Our
findings suggest that in L6 myotubes, 1) atypical PKCs are required and
sufficient for insulin-stimulated GLUT4 translocation and glucose
transport; and 2) activation of protein kinase B in the absence
of activation of atypical PKCs is insufficient for insulin-induced
activation of glucose transport. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Here we used adenoviral gene transfer methodology to introduce various
wild-type and mutant forms of the atypical PKC, PKC-, into L6
myotubes, a continuous cell line derived from rat skeletal muscle. This
approach allowed us to introduce measured, reasonable amounts of these
PKCs into a large fraction of L6 myotubes, and, accordingly, more
critically test the hypothesis that atypical PKCs play an important
role during insulin stimulation of GLUT4 translocation and glucose
transport in this important cell type.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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(provided by Dr. Masato Kasuga, Kobe
University, Kobe, Japan) as described previously in studies of 3T3/L1
adipocytes (11). At the end of the 48-h period, which
allowed sufficient time for expression of encoded PKCs, as described
previously (2), cells were equilibrated at 37 C in
glucose-free Krebs-Ringer phosphate buffer (KRP) containing 1 mg/ml BSA
and then treated with or without insulin as described in the text.
Studies of glucose transport
After insulin treatment for 30 min, the uptake of
[3H]2-deoxyglucose over 5 min and the recovery
of immunoreactive GLUT4 in the plasma membrane (purified by
ultracentrifugation) were measured as described previously
(2). [3H]2-deoxyglucose uptake
results are expressed as counts per min/well. Note that infection of
myotubes with adenovirus alone or adenovirus encoding wild-type,
constitutively active, or kinase-defective PKC- did not alter the
recovery of cellular protein per well or per plate and additionally,
except for adenovirus encoding constitutively active PKC- (which
provoked increases in uptake; see below), did not alter the level of
basal [3H]2-deoxyglucose uptake.
PKC-
/ assays
Activation of PKC-/ was assessed as described previously
(1, 2, 3, 4). In brief, after activation of cells with or
without insulin for 10 min, PKC-/ was immunoprecipitated from
postnuclear (centrifuged at 700 x g for 10 min to
remove nuclei, cellular debris, and floating fat) cell lysates with a
rabbit polyclonal antiserum (Santa Cruz Biotechnology, Inc., Santa Cruz, CA) that targets the nearly identical
C-termini of both PKC- and PKC-. Immunoprecipitates were
collected on protein A-Sepharose G beads, washed, and incubated for 8
min at 30 C in 100 µl buffer containing 50 mM
Tris-HCl (pH 7.5), 5 mM
MgCl2, 100 µM
Na3VO4, 100
µM
Na4P2O7,
1 mM NaF, 100 µM
phenylmethylsulfonylfluoride, 4 µg phosphatidylserine, 3–5 µCi
[
-32P]ATP (NEN Life Science Products, Boston, MA), 50 µM ATP, and,
as substrate, 40 µM PKC-
pseudosubstrate
serine 159 analog (Biosource Technologies, Inc.,
Camarillo, CA). After incubation,
32P-labeled substrate was trapped on p81 filter
paper and counted for radioactivity.
PKB assays
Activation of immunoprecipitable PKB was measured as described
previously (12), using a kit obtained from Upstate Biotechnology, Inc. (Lake Placid, NY).
Western analyses
As previously described (1, 2, 3, 4), cell lysates or
subcellular fractions were boiled and stored in Laemmli buffer,
subjected to SDS-PAGE, transferred to nitrocellulose membranes, and
immunoblotted with the following: 1) rabbit polyclonal antiserum that
targets the C-termini of both PKC- and PKC- (Santa Cruz Biotechnology, Inc.), 2) rabbit polyclonal anti-PKB antiserum
(Upstate Biotechnology, Inc.), 3) rabbit polyclonal
anti-GLUT4 antiserum (Biogenesis, Bournemouth, UK), 4)
rabbit polyclonal anti-GLUT1 antiserum (provided by Dr. Ian Simpson),
5) rabbit polyclonal antiserum that targets the surrounding peptide
sequence that includes phosphoserine 473 in PKB (New England Biolabs, Inc.), 6) goat polyclonal antiserum that recognizes a
specific N-terminal sequence of PKC- (Santa Cruz Biotechnology, Inc.), and 7) mouse monoclonal antibody that
recognizes a specific internal sequence of PKC- (Transduction Laboratories, Inc., Lexington, KY). Immunoblots were quantitated
by measurement of chemiluminescence in a Bio-Rad Laboratories, Inc., Molecular Analyst Chemiluminescence/Phosphorescence
Imaging System (Richmond, CA).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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in adenovirus-infected myotubes
, there were no
significant changes in the level of endogenous 75-kDa PKC-/ in
cells infected with adenovirus alone. In cells infected with adenovirus
encoding wild-type, constitutively active, and kinase-defective
PKC-, there were dose-related increases in the expression of these
PKCs (Fig. 1). In cells infected with adenovirus encoding wild-type and
constitutively active PKC-, total cellular combined PKC-/
(endogenous) plus PKC- (virus-derived exogenous) was increased
approximately 2-fold (i.e. a 100% increase relative to the
endogenous PKC-/) at 5–10 MOI adenovirus in the experiment
depicted in Fig. 1. Note that constitutively active PKC- lacks
N-terminal amino acids 1–135 (which contain the autoinhibitory
pseudosubstrate sequence) and therefore migrates faster than endogenous
or wild-type 75-kDa PKC-/, i.e. at approximately 63
kDa. Also note that in other studies (see Ref. 12 and
unpublished observations), we found that truncated forms of atypical
PKCs are partially activated, but nevertheless can be further activated
by insulin, most likely via increases in PI
3-kinase/3-phosphoinositide-dependent protein kinase-1-dependent
phosphorylation of the threonine 410 loop site and subsequent
autophosphorylation of threonine 560. In cells infected with adenovirus
encoding kinase-defective PKC-, increases in total cellular
PKC-/ were approximately 4.5- to 5.3-fold at 5 and 10 MOI in the
experiment depicted in Fig. 1. In multiple experiments, ratios
(mean ± SE) of total endogenous plus
exogenous PKC-/ to endogenous PKC-/ in cells infected with
10 MOI adenovirus encoding wild-type, constitutively acting, and
kinase-defective PKC- were 2.91 ± 0.52 (n = 7), 3.84
± 0.67 (n = 16), and 3.19 ± 0.33 (n = 16),
respectively.
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, rat-derived L6
myotubes, like rat vastus lateralis skeletal muscle, were found to
contain primarily PKC- and a relatively small amount of PKC-
compared with mouse skeletal muscle, which contained primarily PKC-
and a relatively small amount of PKC-. As reported previously
(12), PKC- and PKC- are closely (72%) homologous
(13), contain the same pseudosubstrate sequence, are
activated similarly by insulin through PI 3-kinase- dependent
increases in
PI-3,4,5-(PO4)3
(12), and, moreover, function interchangeably in
supporting insulin-dependent GLUT4 translocation
(4). The latter interchangeability allowed us to use
PKC- constructs despite the fact that PKC- is the predominant
atypical PKC in L6 myotubes. In confirmation of this assumption of
interchangeability, as described below, mutant forms of PKC- were
indeed found to markedly alter PKC- enzyme activity and insulin
effects on GLUT4 translocation and glucose transport in L6
myotubes.
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on glucose
transport). Expression of wild-type PKC- in
virus-infected myotubes had little or no effect on basal glucose
transport (i.e. 2-deoxyglucose uptake), but at viral doses
of 5–10 MOI it consistently enhanced both maximal and half-maximal
effects of insulin on glucose transport (Figs. 3 and 4). Expression of increasing amounts of
truncated, constitutively active PKC- provoked dose-related
increases in basal glucose transport, and at adenoviral doses of 10 MOI
and higher, basal transport activity approached that observed with
insulin treatment (Fig. 3). Perhaps most importantly, expression of
kinase-defective PKC- at adenoviral doses of 5–10 MOI completely
inhibited the effects of insulin on glucose transport, but had little
or no effect on basal glucose transport (Figs. 3 and 4).
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could not be explained by alterations in cell
recovery (see Materials and Methods) or levels of GLUT1 or
GLUT4 glucose transporters. Indeed, as shown in Fig. 5, the levels of both transporters were
increased significantly by expression of kinase-defective PKC- and,
if anything, were decreased, albeit not statistically significantly, by
expression of constitutively active PKC-.
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on PKC-/
enzyme activity/ enzyme activity (Fig. 6). The expression of kinase-defective
PKC- in virus-infected myotubes led to a decrease in overall
intrinsic enzyme activity of basal PKC-/ (Fig. 6A); this probably
reflects the fact that these immunoprecipitates contained both
enzymatically active endogenous wild-type PKC-/ and virus-derived
kinase-defective PKC-, so the data in Fig. 6A were normalized to
reflect the enzyme activity of equal amounts of immunoprecipitated
PKC-/. Moreover, in cells expressing kinase-defective PKC-,
there was not only a loss of the ability of insulin to provoke
increases in overall PKC-/ activity, but, for uncertain reasons,
PKC-/ enzyme activity actually decreased after insulin treatment
(Fig. 6). We thought it important to assay total combined endogenous
plus exogenous virus-derived atypical PKC enzyme activity, rather than
endogenous PKC-/ activity, in these studies, as this mixture of
virus-derived exogenous PKC- plus endogenous PKC-/ is what the
intact virus-infected cell contains and uses to regulate biological
processes. In this context, the virus-derived kinase-defective PKC-
would be expected to compete with endogenous wild-type atypical PKCs
for activating factors and substrates in both intact cells and in the
assay in vitro. Indeed, we previously reported that in rat
adipocytes (which, like rat skeletal muscles and rat-derived L6
myotubes, contain primarily PKC-), 1) plasmid-mediated expression of
kinase-inactive forms of either PKC- or PKC- leads to inhibition
of total cellular, combined (endogenous plus exogenous),
insulin-stimulated, immunoprecipitable PKC-/ (4);
and 2) plasmid-mediated expression of both kinase-inactive and
activation-resistant (threonine 410 mutated to alanine) forms of
PKC- inhibits insulin-induced activation of epitope-tagged wild-type
PKC- (14). In addition, assuming that total atypical
PKC enzyme activity in cells expressing kinase-defective PKC-
largely reflects that of the enzymatically active, endogenous PKC-
(see above), from the data shown in Fig. 6, it seems clear that
kinase-defective PKC- served as a very effective inhibitor of
insulin-induced activation of this endogenous PKC- in L6
myotubes.
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, expression of constitutively
active PKC- was attended by the anticipated increases in the
intrinsic enzyme activity of PKC-/ immunoprecipitated from
lysates of control myotubes (Fig. 6A
). In addition to increasing basal
intrinsic PKC-/ enzyme activity, the total cellular content of
enzymatically active PKC-/, i.e. endogenous wild-type
PKC-/ plus virus-derived, constitutively active PKC-, was
increased substantially (see Fig. 6C), and total cellular basal
PKC-/ enzyme activity was increased approximately 4-fold in cells
infected with adenovirus encoding constitutively active PKC- (Fig. 6B). Nevertheless, insulin continued to provoke increases in
PKC-/ enzyme activity in cells infected with constituitively
active PKC- (Fig. 6), and this probably reflects 1) the
activation of endogenous wild-type PKC-/, and/or 2) the
fact that N-terminally truncated forms of atypical PKCs are only
partially activated and can be further activated by insulin, most
likely via 3-phosphoinositide-dependent kinase-1 increases in
phosphorylation (12) (our unpublished
observations).
Effects of expression of kinase-defective PKC- on PKB
activity
As PKB has been reported to be required for insulin- induced
translocation of epitope-tagged GLUT4 glucose transporter to the plasma
membrane and presumably for subsequent glucose transport in L6 myotubes
(8), it was important to determine whether
kinase-defective PKC- interfered with insulin-induced activation of
PKB. On the contrary, expression of kinase-defective PKC- was
attended by increases in insulin-stimulated PKB enzyme activity (Fig. 7) and PKB/serine 473 phosphorylation
(Figs. 7 and 8). This finding of
increased PKB activation/phosphorylation may be due in part to
increases in immunoreactive PKB content (Figs. 7 and 8), but may also
reflect the fact that atypical PKCs can act as negative modulators of
PKB (15). Whatever the correct explanation, the presently
observed inhibitory effects of kinase-defective PKC- on glucose
transport cannot be explained by inhibition of PKB.
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on GLUT4
translocation to the plasma membrane in adenovirus-infected myotubes provoked
qualitatively similar changes in the recovery of immunoreactive GLUT4
in the plasma membrane. As shown in Fig. 8, in cells infected with
virus alone, there was little or no GLUT4 recovered in the plasma
membrane fraction in the basal state, and insulin provoked a marked
increase in plasma membrane GLUT4 content. In myotubes expressing
wild-type PKC-, the basal level of plasma membrane GLUT4 was
surprisingly high (Fig. 8) despite the fact that there was no
concomitant increase in basal glucose transport (see Figs. 3 and 4).
This apparent disparity may reflect the fact that actual glucose
transport may be dependent not only on the plasma membrane level of
GLUT4, but also on other insulin-induced factors that appear to be
required to increase the transport activity of plasma
membrane-associated GLUT4 (16, 17). Alternatively, it is
possible that there may be both functional and nonfunctional pools of
plasma membrane-associated GLUT4. Nevertheless, despite increased basal
levels, insulin provoked further increases in plasma membrane GLUT4
levels in cells expressing wild-type PKC-. Moreover, in myotubes
expressing constitutively active PKC-, basal plasma membrane GLUT4
levels were increased to virtually the same extent as that observed
with insulin (Fig. 8). And, perhaps most importantly, in myotubes
expressing kinase-defective PKC-, insulin failed to provoke
increases in plasma membrane GLUT4 content (Fig. 8). |
Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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that led to essentially complete
inhibition of the effects of insulin on both GLUT4 translocation and
glucose transport, viz. at a viral titer of 5–10 MOI, was
approximately 3- to 4-fold greater than the level of endogenous
PKC-/. Assuming that expression of a given amount of
kinase-defective (i.e. inactive) atypical PKC would
effectively dilute the enzymatic and biological activity of an equal
amount of endogenous atypical PKC by 50%, a 4-fold excess of
kinase-defective atypical PKC would be expected to inhibit endogenous
atypical PKC by approximately 80%, i.e. slightly less than
the virtually complete inhibition of insulin-stimulated GLUT4
translocation and glucose transport presently observed. This disparity
may reflect the fact that total cellular PKC-/ enzyme activity
was paradoxically diminished by insulin treatment in cells expressing
kinase-defective PKC-.
Dependency of endogenous GLUT4 translocation and overall glucose
transport has also been reported in adenoviral gene transfer studies in
3T3/L1 adipocytes (11). However, in 3T3/L1 cells, the
maximal level of inhibition of GLUT4 translocation and glucose
transport caused by expression of kinase-defective PKC- was
approximately 50–60% compared with the virtually complete inhibition
we observed in L6 myotubes. As the 3T3/L1 adipocytes and L6 myotubes
used in these studies were transfected with saturating amounts of the
same adenoviral PKC- constructs, it is possible that despite partial
similarities, the signaling factors used by insulin to activate
GLUT4/glucose transport systems may be partly different in these two
cell types. However, another possibility is that lesser inhibitory
effects of kinase-defective PKC- on insulin-stimulated glucose
transport in 3T3/L1 adipocytes may reflect lesser rates of adenoviral
infection in these cells.
In addition to the apparent requirement for atypical PKCs during
insulin-stimulated GLUT4 translocation and glucose transport in L6
myotubes (as suggested by studies with kinase-defective PKC-), the
fact that expression of wild-type PKC- potentiated insulin effects
suggested that atypical PKCs actively contribute to insulin-stimulated
GLUT4 translocation and glucose transport. Interestingly, similar
potentiating effects of overexpressed wild-type PKC- on
insulin-stimulated epitope-tagged GLUT4 translocation or glucose
transport have been observed in transiently transfected rat adipocytes
(4) and in rat skeletal muscles injected in
vivo with adenovirus encoding wild-type PKC- (18).
In keeping with the possibility that PKC-/ contributes to
insulin-stimulated glucose transport, it may be noted that even in the
absence of insulin treatment, constitutively active PKC- was capable
of provoking increases in GLUT4 translocation and glucose transport
comparable to those of insulin. On the other hand, it is questionable
if the expression of a constitutively active atypical PKC truly mimics
the signaling system(s) used by insulin in intact cells.
The present findings are in agreement with those of our previous
studies that suggested a requirement for atypical PKCs during
insulin-stimulated GLUT4 translocation and glucose transport in L6
myotubes (2), 3T3/L1 adipocytes (1), and rat
adipocytes (3, 4). However, the presently used adenoviral
gene transfer methodology provided more convincing evidence for this
hypothesis than the stable and transient transfection methodology used
in our previous studies. In this regard, stable transfection approaches
are open to the criticisms that they do not necessarily provide a
homogeneous population of uniformly transfected cells and, moreover,
may select cells that employ aberrant signaling circuits. In both L6
myotubes (2) and 3T3/L1 cells (1), for
example, the stable transfection approach yielded cell populations in
which expression of kinase-defective PKC- inhibited
insulin-stimulated glucose transport and GLUT4 translocation to the
plasma membrane by only 50%, and it was uncertain whether this
reflected a failure to obtain cells that were uniformly transfected,
the possibility that there was only a 2-fold increase in total
PKC-/ levels in uniformly transfected cells, or the existence of
multiple parallel mechanisms used by insulin to activate the glucose
transport system. Similarly, in transient transfections, an even
smaller percentage of cells was successfully transfected, and it was
generally necessary to use an exogenously cotransfected epitope-tagged
GLUT4 or another extraneous marker to focus on successfully transfected
cells. Obviously, there are many assumptions in the transient
cotransfection approach, e.g. that cotransfections have
occurred in the same cell population, and even if all assumptions are
correct, this approach does not provide direct information on the
endogenous glucose transport system. Moreover, in the transient
transfection approach, particularly at low transfection rates, it is
generally necessary to use relatively large amounts of plasmid to be
certain that significant protein expression has occurred, and this not
only leads to excessive amounts of wild-type or mutant protein in
successfully transfected cells, but also is attended by considerable
uncertainty as to the ratio of transfected protein to the endogenous
protein under study. Obviously, we were able to avoid many of these
caveats in the present adenoviral gene transfer studies.
It was of interest that there appeared to be an inverse relationship
between PKC-/ enzyme activity and levels of GLUT4 and GLUT1
glucose transporters. Thus, expression of constitutively active PKC-
was attended by mild, but statistically insignificant, decreases in the
levels of these transporters, and expression of kinase-defective
PKC- was attended by more substantial, statistically significant,
increases in levels of these transporters. A similar inverse
relationship between PKC- enzyme activity and glucose transporter
levels was also observed in previous stable transfection studies in
3T3/L1 adipocytes (1) and L6 myotubes (2),
and this relationship may reflect a homeostatic mechanism that attempts
to maintain a sufficient, but not excessive, level of glucose
transport.
It was of interest to find that despite enhanced effects of insulin on
PKB phosphorylation and activation in cells expressing kinase-defective
PKC-, insulin was unable to stimulate GLUT4 translocation or glucose
transport. This finding provided clear evidence that the activation of
PKB in the absence of atypical PKC activation is not sufficient for
activation of the insulin-dependent glucose transport system, and
activation of an atypical PKC may be indispensable for this action of
insulin in L6 myotubes. This does not necessarily imply that PKB is not
required for insulin-stimulated glucose transport in these cells.
Indeed, the findings of Akimoto et al. (13)
suggest that PKB is required for insulin-stimulated GLUT4 translocation
in L6 myotubes. Accordingly, at this point, it appears that both PKB
and atypical PKCs are required for insulin-stimulated glucose transport
in L6 myotubes.
In summary, we used adenoviral gene transfer methods to introduce
various forms of PKC- into L6 myotubes to examine the role of
atypical PKCs during insulin stimulation of endogenous GLUT4
translocation and glucose transport. We found that expression of
kinase-defective PKC- completely inhibited, wild-type PKC-
potentiated, and constitutively active PKC- fully mimicked the
effects of insulin on GLUT4 translocation and glucose transport. Our
findings provided strong support for the hypothesis that atypical PKCs
are required for and contribute directly to the effects of insulin on
GLUT4 translocation and glucose transport in the L6 skeletal muscle
cell line.
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Acknowledgments |
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Footnotes |
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Received May 1, 2000.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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, ß, and ) by insulin in 3T3/L1
cells. Transfection studies suggest a role for PKC- in glucose
transport. J Biol Chem 272:2551–2558 and noninvolvement of diacylglycerol-sensitive PKCs in
insulin-stimulated glucose transport in L6 myotubes. Endocrinology 138:4721–4731 as a downstream
effector of phosphatidylinositol 3-kinase during insulin stimulation in
rat adipocytes. Potential role in glucose transport. J Biol Chem 272:30075–20082,
), conventional (, ß) and novel (
, ) protein kinase C
isoforms on insulin-stimulated translocation of epitope-tagged GlUT4
glucose transporters in rat adipocytes: specific interchangeable
effects of protein kinases C- and C-. Biochem J 337:461–470
-q/11 protein plays a key role in insulin-induced glucose transport
in 3T3/L1 adipocytes. J Biol Chem 274:33691–33695 for insulin stimulation of
glucose uptake but not for Akt activation in 3T3–L1 adipocytes. Mol
Cell Biol 18:6972–6982
and
C- by an autophosphorylation-dependent mechanism and stimulates
their translocation to GLUT4 vesicles and other membrane fractions in
rat adipocytes. J Biol Chem 274:25308–25316, expressed dominantly in an undifferentiated
mouse embryonal carcinoma cell line and also in many tissues and cells.
J Biol Chem 269:12677–12683. Mol Endocrinol 13:1766–1772 is a negative regulator of protein kinase B
activity. J Biol Chem 274:8589–8596
stimulates glucose transport activity in rat skeletal muscle. J
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P. Weyrich, K. Kapp, G. Niederfellner, M. Melzer, R. Lehmann, H.-U. Haring, and R. Lammers Partitioning-Defective Protein 6 Regulates Insulin-Dependent Glycogen Synthesis via Atypical Protein Kinase C Mol. Endocrinol., May 1, 2004; 18(5): 1287 - 1300. [Abstract] [Full Text] [PDF]
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) or
without (
) 100 nM insulin, after which uptake of
[3H]2-deoxyglucose over 5 min was measured. Note that
adenoviral constructs did not alter cellular protein content per well.
Shown here are the mean ± SE for three or more
determinations (n = 3–12) or the mean ± range for two
determinations (n = 2). Asterisks indicate P
< 0.005, as determined by t test comparisons of peak
alterations: a, insulin-stimulated value at 10 MOI virus encoding
wild-type PKC-
).
